The apparatus disclosed herein is essentially an improvement to applicant's piston connecting rod assembly indicated above, the entirety of which is incorporated herein by reference.
The prior application discloses an apparatus for providing constant volume combustion (CVC) in a two-stroke or four-stroke internal combustion engine. With constant volume combustion, the entire fuel-air mixture burns before the piston makes any substantial movement downward. Without CVC, a portion of the fuel remains unburned until after the piston has moved a distance downward. This remaining portion of the combustion produces less mechanical work and greater exhaust waste heat, worsening efficiency and thermal concerns. In addition, without CVC some fuel may not be completely burned, resulting in higher concentrations of hydrocarbons, carbon monoxide and other undesirable pollutants in the exhaust gas. The emission problems due to the late or incomplete burning of fuel in a non-CVC engine are worsened by the fact that the expansion of the combustion chamber cools the gases contained therein due to the ideal gas law, further slowing the rate of combustion and delaying the combustion of remaining fuel.
Normally, in a conventional piston engine, the piston follows a sinusoidal path as the crank shaft rotates. Thus, the piston is stationary only momentarily when at top dead center (TDC) and bottom dead center (BDC). At full compression, the volume of the combustion chamber above the piston has a substantially constant (and minimum) volume during only a small portion of the angular rotation of the crank. Particularly at high crank rotation rates, this is an insufficient interval to provide complete combustion of the fuel at a constant volume.
In applicant's previous apparatus described in the application noted above, complete constant volume combustion is achieved with a connecting rod that provides added distance between the crank and the piston as the connecting rod is pivoted with respect to the piston. Effectively, the rod pushes the piston away as the crank pivots the rod past TDC, with the pushing away serving to counteract for a time the initial downward motion of the piston. This is achieved by a curvilinear cam groove engaged by a pin on the piston. The net effect provides constant volume combustion by combining a small cyclical vertical motion of the piston relative to the connecting rod with the conventional sinusoidal motion of the piston. As a result, the normal sinusoidal peaks of a conventional engine are flattened and extended to form plateaus; as the piston pauses or dwells without substantial downward motion for a time after the crank passes TDC. During this period, the combustion chamber volume is substantially constant. These plateaus have a sufficient width, that is, the piston dwell time after TDC is sufficient for the fuel mixture to be entirely burned.
Although the prior art apparatus is effective to provide fuel efficient and clean combustion, particularly with two-stroke engines, it has several functional limitations:
A first limitation of the prior art apparatus is that it is susceptible to wear, particularly at the cam groove. Substantially all of the explosive force of the engine is transmitted to the crank shaft by a pin on the piston that engages the cam groove. The high frictional loading pressures at this interface causes unavoidable wear that eventually degrades performance and decreases life expectancy.
A second limitation of the prior art apparatus is the high manufacturing cost needed to maximize the wearresistance of the components. To get maximum life expectancy from the connecting rod crank, the forged rod must be cut, ground and polished at the cam groove. These multiple manufacturing steps increase manufacturing costs. In addition, the cam groove has a particular irregular shape to provide the proper piston motion profile. This shape requires precise machining to give optimum performance.
A third limitation of the prior art apparatus is that a single connecting rod cam groove design achieves only a single piston motion profile. Therefore, if the engine is to be converted to an alternative fuel, new connecting rods must be designed, manufactured and installed. In addition, for a single fuel, the piston motion profile must be selected to provide an adequate compromise of performance at various crank shaft rotation rates. A profile optimized for slower rotation rates may not achieve constant volume combustion at higher rotation rates because the increased angular velocity of the crank shaft affords less actual time at constant volume for the fuel to burn. A profile optimized for high RPMs may result in excessive dwell that increases internal mechanical stresses and impairs efficiency.